1. Field of Invention
The present invention relates to a method and a system for diagnosing a common rail diesel engine that can sense and diagnose a fuel leak from a fuel supply system of the common rail diesel engine.
2. Description of Related Art
As is generally known, a common rail diesel engine is a scheme that directly injects fuel into a combustion chamber unlike an existing engine which is a scheme that supplies fuel and air to the combustion chamber through a mixer.
For example, a diesel fuel injecting device which has been used up to now is a scheme that uses a cam driving device in order to acquire injection pressure and has a principle in which the injection pressure increases together with an increase of velocity, and as a result, an injection fuel amount increases.
However, a common rail scheme according to the present invention has an advantage in that generation of injection pressure and an injection process are separated from each other such that pressure generation and injection of fuel may be separately considered in designing an engine, and as a result, combustion and injection processes may be freely designed.
That is, in the common rail diesel engine, since fuel pressure and a fuel injection time may be adjusted according to an engine operating condition by using an engine map, even when an rpm of the engine is low, high-pressure injection is enabled, and as a result, complete combustion may be pursued, exhaustion and noise may be minimized, and fuel efficiency may be significantly improved.
Referring to a configuration of a common rail diesel engine, fuel in a fuel tank 2 is pumped by a high-pressure fuel pump 4 and supplied to a common rail 6, as illustrated in FIG. 1. Fuel which is supplied to the common rail 6 while keeping predetermined pressure is injected into the combustion chamber through a fuel injector 8.
The high-pressure fuel pump 4 serves to pump fuel while being driven by a cam shaft and pressure in the common rail 6 is sensed by a pressure sensor 10. An engine control device 20 controls a pressure control valve 12, which is placed in an outlet of the high-pressure fuel pump 4, according to the rpm and a load of the engine, so as to continuously control fuel to a set value without compressing the fuel at high pressure while rotating the engine.
However, in the existing common rail diesel engine, when a small amount of fuel leaks from a common rail 10 and/or a connection rail, a change in pressure sensed by the pressure sensor 10 is slight, and as a result, there is a limit in diagnosing the fuel leak.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.